The present invention concerns a track brake, especially a grade-compensating track brake for braking railroad vehicles, with at least one piston track brake against the rail and with a device actuated by a shifting mechanism and shifting the piston track brake out of an active and into an inactive state.
Grade-compensating track brakes are employed when there is a grade in the train-assembly sidings in shunting yards that is too steep for the coasting resistance of the individual cars.
A car, decelerated by track brakes at the beginning of a train-assembly siding, will accelerate to unacceptable speeds and can inflict considerable damage on the other cars or on the freight as it strikes against them.
A track brake of the aforesaid genus is known from German 19 635 487. The piston track brake itself is described in German 3 031 173. The piston track brakes in the known track brakes are distributed along the rail and can pivot subject to a shifting mechanism between an active and an inactive state around an axis paralleling the rail. The piston track brake can be pivoted into an inactive state at any time, even when some car wheels are within a braking section. The piston track brakes, however, can only be shifted into the active state when no wheels are in a braking section. This feature prevents the piston track brakes from being forced against the wheels. Each braking section must accordingly also be monitored by track-switching sensors in the form of track circuits for example. This approach is expensive
Embodiments are known in practice that include a pneumatic piston-and-cylinder mechanism paralleling a tube that travels back and forth along the piston track brake. The end of the pneumatic mechanism""s piston is hooked and engages the head of the tube. A hydraulic piston-and-cylinder mechanism or small shifting mechanism can be employed instead of the pneumatic mechanism. Whatever version is employed, the hooked end of a piston draws the tube in or lowers it. Power can be supplied to the individual piston track brakes or to groups of ten for example thereof. This embodiment allows a piston track brake to shifted into an active or inactive state even when the wheels are within a braking section. There is, however, a drawback to this system in that it requires several components that must be mounted on the piston track brake""s housing. These components must be able to accommodate the extremely high accelerating forces that occur when the wheels strike the heads of the piston tube. Impacts 1000 times the acceleration of gravity have been measured. Practice has demonstrated that such accelerations considerably increase wear and accordingly costs while severely limiting performance. This embodiment is accordingly not way-stable and is particularly impractical for rough railroading.
The object of the present invention is to improve a track brake of the aforesaid genus to the extent that the piston track brakes can be shifted out of the inactive and into the active state even when there are car wheels in the braking section while simultaneously improving overall performance and ensuring a way-stable and robust structure.
This object is attained in accordance with the present invention in a generic track brake in that the aforesaid track-brake shifting device is a track-brake lowering device with a length of structural section that extends along the piston track brakes and has drag bars attached to it that engage the piston track brakes. The track-brake lowering brake is on the same level as the head of the piston tube. The piston track brake itself does not need to be modified. The drag bars extend over the piston-tube heads and, when the track-brake lowering brake is actuated, force the piston tubes down against their inherent shock-absorption resilience until the heads assume a position wherein they are no longer impacted by the car wheels. In this state the track brake will be inactive and the railroad vehicle can pass over it unimpeded.
The length of structural section in one preferred embodiment of the present invention rotates around its longitudinal axis. The length of structural section can be round or polygonal. The shifting mechanism can preferably be a tubular motor. Such other mechanisms as a linear drive with a cable and deflection roller can also be employed to rotate the section between an active and an inactive state, into the active state subject to resilient shock-absorption forces on the drag bars when the linear drive releases the cable. To shift it into the inactive state, the section is rotated when the cable is shortened by the displacement of the linear drive. A chain drive with a motor accommodated in the rail as in an overhead door can also be employed.
The length of structural section and/or the motor in this preferred embodiment can be provided with bearing pins that rest in associated bearings. It is practical for the bearings to be mounted on angle irons secured to the rail and in particular to their webs. It is essential to the performance of the track brake that the drag bars be outside the space needed to control the vehicle while still engaging the piston-tube heads when the track-brake lowering brake is in the active state. Performance will also be improved if the end of the drag bars that engages the piston track brake is provided with a round-off that allows them to roll over the upper surface of the piston-tube heads as the length of structural section rotates.
It will be practical for the length of structural section to be located along with the drag bars between the middle of the rail and the piston track brake in the path of the piston tube as it rises.
The drag bars in a further embodiment of the present invention can be fastened to the length of structural section by threaded bolts and cup springs tensioned thereby. The advantage is that drag bars that are easy to replace will protect the shifting mechanism from impact. Such impacts occur when cars are being rolled over a braking-section while the track-brake lowering brake is active and the drag bars are being engaged in a half-way position by rapidly moving piston tubes. It is practical for the drag bars to be of hardened slab steel approximately 10-20 mm thick and approximately 70-120 mm wide. The bars should be approximately 100-200 mm long in order to overlap the piston-tube heads sufficiently when the distances between the piston track brakes vary considerably.
The length of structural section in the track-brake lowering brake can just as well rise as rotate. In this event, the length of structural section can be provided with upright guides and/or lifting mechanisms in the form of threaded shafts or hydraulic piston-and-cylinder mechanisms, allowing the section and its drag bars to raise and lower the piston tubes.
Adjustable limiting switches can also be employed to monitor and vary the active and inactive states of the piston track brake, along with a maintenance state.
It can also be of benefit for the length of structural section to telescope along the piston track-brake and/or for the drag bars to be tensioned on at any desired locations or at any desired intervals along it.
When a grade-compensating brake in accordance with the present invention is installed, bores can be drilled in the track web between the ties to accommodate the piston track brake and the angle irons in the track-brake lowering brake without taking the distances between ties into consideration. Once the piston track brake has been screwed on, the telescoping structural section can be screwed into place by extending it until its two angle irons are aligned with their bores. The drag bars can then be aligned and fastened to the section in accordance with the actual installed position of thr piston track brakes. Modifications in the superstructure of thr train-assembly siding to adapt it to the intervals between ties will not be necessary in accordance with the present invention. It is also possible in accordance with the present invention to employ a telescoping section by itself or, when a telescoping section is not employed, to tension the drag bars to the section at any desired points.
The telescoping section cam comprise two or more square or otherwise polygonal lengths, one sliding in and out of the other. It is important in this event to prevent the inner length from rotating inside the outer length. Bearing pins and bearings can be positioned at either head of the lengths and screwed to the angle irons. The telescoping section can easily be adjusted in length to conform to the varying distances of the screws that secure the angle irons before it is screwed tight.
The drag bars can preferably be tensioned to the structural section with U-shaped clamps that conform to its outer contour. The drag bars can be angled, one arm contacting the piston track brake""s piston tube by way of a small roller. The other arm can constitute a base plate and rest against one side of the telescoping section. The edges of the base plate extend beyond the telescoping section to allow the open ends of the U-shaped clamps to be screwed to the base plate. The open ends of two of the U-shaped clamps that conform to the contour of the structural section can be threaded, allowing them to screw into the base plate and accordingly tension the drag bars at any desired points along the section. Piston track brakes installed at very different positions can accordingly be equalized without additional expenditure.
In one preferred embodiment of the present invention one or more shock-absorbing plates can be interposed between the drag bar""s base plate and one side of the telescoping section, attenuating any impact stresses that may occur. The telescoping section can also be multiple-stage or be at each end of a length of structural section.
The advantages attained in accordance with the present invention will now be summarized. The piston track brakes can be employed either when they are forced down directly by a railroad-car wheel or when they cannot be shifted out of an inactive and into an active state and vice versa. When one piston track brake is prevented from automatically shifting its state by a wheel resting above it, the track-brake lowering brake can still be acuated, allowing all the other to shift into the active state. Since the drag bars and the length of structural section are located outside the space needed to control the car, they will not come into contact with the car""s wheels. The braking section will not need to be monitored by rail-switching sensors.